The thermal flow sensor which measures the flow rate of a gas includes a flow rate detection section to measure a flow rate and is arranged such that the flow rate of the gas is measured through the thermal transmission being conducted between the flow rate detection section and the gas which is an object to be measured. The flow rates measured by the thermal flow sensor are widely put to use as the parameters important to control various types of devices. The characteristic feature of the thermal flow sensor lies in that it can measure the flow rate of a gas with relatively higher precision than the other flow sensors operated according to different methods, but in recent years it is hoped that the precision with which the flow rate of a gas is measured is further enhanced. For instance, with a vehicle in which an internal combustion engine is incorporated, further enhancement of fuel saving and exhausted gas purification is on high demand. In order to respond to such demand, it is required that the intake air volume which is a principal parameter of the internal combustion engine be measured with enhanced precision. The thermal flow sensor which measures the volume of an intake air guided into the internal combustion engine includes an auxiliary channel to take in a portion of the intake air volume and a flow rate detection section disposed in the auxiliary channel, in which the flow rate detection section measures the state of a gas to be measured which flows through the auxiliary channel through the thermal transmission being conducted between the flow rate detection section and the gas to be measured and outputs an electric signal defining the volume of an intake air guided into the internal combustion engine. The above-mentioned thermal flow sensor is disclosed in Japanese Patent Application Laid-Open Publication No. 2011-252796 (PTL 1), by way of one example.
Further, regarding such measuring instruments as the above-mentioned thermal flow sensor, it is disclosed in Japanese Patent Application Laid-Open No. HEI 11 (1999)-258019 (PLT 2), by way of one example that in order to prevent the base and the cover bonded through an adhesive and as such on the housing to receive a measuring device therein from being peeled off from the housing owing to the deterioration of adhesive strength and from being dropped into the main channel, they are fused to the housing with the provision of the drop-off prevention projection and the drop-off prevention groove. Further, the laser-welding technique in which the housing and the cover are laser-welded to each other is disclosed in Japanese Patent Application Laid-Open No. 2007-210165 (PTL 3), by way of one example. Moreover, in Japanese Patent Unexamined Application Publication No. 2008-260161 (PTL 4), there is disclosure that in order to restrain burrs generated when the laser-welding is performed from being dropped off, a closure space in which such burrs are received is formed. Furthermore, in Japanese Patent Application Laid-Open No. 2010-221572 (PTL 5), there is disclosure on the technique by which the fused resin is not oozed out of the main body through a groove being provided on each end of a transmissive resin where a laser beam is irradiated.